1. Field of the Invention
The invention relates to generator stator core removal, and more particularly to field removal and reinstallation of assembled stator cores from non-vertically oriented generator frames, including horizontally-oriented generator frames.
2. Description of the Prior Art
During a generator major overhaul stator cores are removed from the generator frame. Old core windings and insulation are stripped from the stator core lamina stack and replaced with new ones. The replacement stator core is assembled within the generator frame. Generally the overhaul is performed at the power generation site, rather than transporting the entire generator to an offsite repair facility.
Some generator designs facilitate removal of their entire stator core assembly as a module by orienting the core axis in a vertical position and lifting the core module with a crane or other hoisting device that is coupled to a lifting plate affixed to an axial end of the stator core. When vertically lifting an entire stator core module care must be taken to avoid damaging either the core or the generator frame by inadvertent contact during lifting. Given the relatively large diameter, axial length and weight of a stator core, and the relatively small radial clearance with the generator frame a small yaw of the stator core during the hoisting operation may cause inadvertent impacts. Cranes, hoists and similar heavy moving equipment are expensive to purchase or lease, require logistic planning to have them available on a job site and skilled operating engineers, thus often necessitating retention of specialized subcontractors to complete the generator refurbishment. It is desirable to minimize the number of subcontractors needed to refurbish a generator, as well as minimize likelihood of generator damage that might result from impacts incurred during vertical stator core hoisting.
Other generator designs are not suitable for vertically lifting stator cores prior to their refurbishment. In those generator designs the stator core is disassembled in place by hand. Service personnel serially and repetitively remove layers of core windings, insulation and individual core lamina (often up to 75000 individual laminations) in the lamina stack with hand-held tools while the generator frame is oriented with its rotor rotational axis in a vertical or horizontal position (analogous to an archaeological excavation). Such hand labor is time consuming and expensive. A typical in-place rotor core disassembly within the generator frame requires 3-8 days' work by a service crew to remove layers of lamina, windings and insulation. Core disassembly external to the generator consumes less service time, and allows quicker generator service resumption.